1. Field of the Invention
The present invention relates to a pneumatic tire having a tread pattern provided in a tread section.
2. Background Information
Studless tires have been used as a winter tire for some time in Europe and other places. The studless tires are expected to exhibit excellent braking performance on snow covered roads and also need to provide excellent braking performance on damp roads (wet roads) where water has collected on the road surface due to melting snow. That is, studless tires are expected to have excellent braking performance on both snow covered road surfaces and wet road surfaces. Various tread patterns have been proposed for such a studless tire.
For example, a studless tire has been proposed that can improve water drainage while ensuring good snow and ice performance (Japanese Laid-open Patent Publication No. 2002-283812). With this studless tire, the tread contact surface only has a plurality of transverse grooves that transversely cross the treads. Each of the transverse grooves is formed by joining together two crosswise grooves. One of the crosswise grooves extends from one tread border toward a tire equator surface, is substantially not slanted with respect to an axial direction of the tire (tire widthwise direction) at least near the tread border, and is slanted with respect to the tire axial direction at a tread middle portion that is closer to the tire equator surface than a portion near the tread border. The other crosswise groove extends from another tread border toward the tire equator surface and is slanted with respect to the tire axial direction at a tread middle portion that excludes at least a portion near the tread border. At the tread middle portion, each of these transverse grooves forms two branch grooves and the tread middle portion. One of the branch grooves slants in a tire rotational direction with respect to a tire rotational axis, and the other branch groove slants in the opposite direction of the tire rotational direction with respect to the tire rotational axis. A column of a plurality of blocks is formed by the branch grooves extending from opposite tread borders being joined together. Assuming the tire width is divided into eight equal parts from one tread border to the other tread border, then a negative ratio (groove area ratio) of a tread middle region comprising two regions of the tread middle portion is set to be smaller than a negative ratio of a tread side region positioned outward of the tread middle region in the tire axial direction. With a tread pattern configured in this manner, water drainage can be improved while also ensuring good snow and ice performance.